1. Field of the Invention
This invention relates generally to a solid state imager device and is directed more particularly to an interline transfer type solid state imager device which has a light receiving section formed of a buried channel MOS structure.
2. Description of the Prior Art
In a solid state imager device due to its characteristics, it is desirable to reduce, as much as possible the dark current which may be a source of noise.
A conventional solid state imager device which can reduce the dark current, for example, is disclosed in a collection of papers presented at '84 National Conference of the Institute of Television Engineers of Japan, on pages 41-42. Such known solid state imager device has a light receiving section which is formed of a buried channel MOS structure. Specifically, the device is constructed such that an n-type charge storage area is formed over the surface of a p-type silicon substrate and a forward electrode is formed on the charge storage area through an insulating layer, so that it can be operated under conditions where a hole storage layer is produced on a boundary between the n-type charge storage area and the insulating layer. In this solid state imager device, the forward electrode is applied with a predetermined direct current voltage so as to form a channel within the n-type charge storage area from holes previously stored on the surface of the n-type charge storage area. Thus, the holes are kept in a so-called pinning state, so as to suppress the generation of hole-electron pairs which are the main component of the dark current from the surface level. A solid state imager device as described above can advantageously reduce the dark current.
However, such conventional solid state imager device has disadvantages in that since the forward electrode is always supplied with a direct current voltage so as to store holes on the boundary between the n-type charge storage area and the insulating layer, the depletion layer under the charge storage area is not extended making it impossible to suppress disturbances in images which are picked-up, which disturbances are caused by signal charges flowing from the inside of the substrate into the charge transfer section, which are called "smear".